Network analyzers are instruments that characterize networks. The characterization result is based on conventions and define how the network will perform under various conditions. In signal integrity applications, the common network parameters in use are scattering parameters, or s-parameters. S-parameters define port to port relationships in a network when the network is driven by a source whose impedance is set to the reference impedance and all other ports are terminated in that same reference impedance. This convention allows scattering parameters to completely define the behavior of a network under any other driving and termination conditions.
A standard instrument for s-parameter measurement is the vector network analyzer (VNA). This instrument stimulates a network with sinusoidal incident wave-forms and measures the reflected sinusoidal waveforms at the network ports. This instrument is most commonly used in the field of microwave analysis. It is a very expensive instrument.
Another instrument used for s-parameter measurement uses techniques called time domain reflectometry (TDR) and time domain transmission (TDT) (Here we will use the commonly used acronym TDR to represent both techniques, the name of the instrument itself, and time domain analysis in general). TDR stimulates a network with an incident step, or pulse and measures reflected waveforms at the network ports. This instrument is most commonly used in the field of signal integrity. TDR is much less expensive than the VNA and has various advantages and disadvantages compared to the VNA.
Because of their cost, familiarity in the signal integrity field, and other reasons it is advantageous to measure s-parameters using time domain methods.
A well known drawback of time domain methods for s-parameter measurement is lack of dynamic range. While VNAs boast 90-110 decibels (dB) of dynamic range, it has been difficult to produce TDR instruments that can achieve much higher than 40 dB of dynamic range.
What is needed is a time domain s-parameter measurement instrument with higher dynamic range.